package com.yangc.utils.encryption;

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.KeyPairGenerator;
import java.security.NoSuchAlgorithmException;
import java.security.interfaces.RSAPrivateKey;
import java.security.interfaces.RSAPublicKey;
import java.security.spec.InvalidKeySpecException;
import java.security.spec.RSAPrivateKeySpec;
import java.security.spec.RSAPublicKeySpec;
import java.util.HashMap;
import java.util.Map;

import javax.crypto.Cipher;

public class RsaUtils {

	private static final String RSA = "RSA";

	private static final String PUBLIC_KEY = "public";

	private static final String PRIVATE_KEY = "private";

	/**
	 * 生成公钥和私钥
	 */
	public static Map<String, Object> getKeys() {
		try {
			KeyPairGenerator keyPairGen = KeyPairGenerator.getInstance(RSA);
			keyPairGen.initialize(1024);
			KeyPair keyPair = keyPairGen.generateKeyPair();
			RSAPublicKey publicKey = (RSAPublicKey) keyPair.getPublic();
			RSAPrivateKey privateKey = (RSAPrivateKey) keyPair.getPrivate();
			Map<String, Object> map = new HashMap<String, Object>();
			map.put(PUBLIC_KEY, publicKey);
			map.put(PRIVATE_KEY, privateKey);
			return map;
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		}
		return null;
	}

	/**
	 * 使用模和指数生成RSA公钥 注意：【此代码用了默认补位方式，为RSA/None/PKCS1Padding，不同JDK默认的补位方式可能不同，如Android默认是RSA/None/NoPadding】
	 * @param modulus 模
	 * @param exponent 指数
	 * @return
	 */
	public static RSAPublicKey getPublicKey(String modulus, String exponent) {
		try {
			BigInteger b1 = new BigInteger(modulus);
			BigInteger b2 = new BigInteger(exponent);
			KeyFactory keyFactory = KeyFactory.getInstance(RSA);
			RSAPublicKeySpec keySpec = new RSAPublicKeySpec(b1, b2);
			return (RSAPublicKey) keyFactory.generatePublic(keySpec);
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		} catch (InvalidKeySpecException e) {
			e.printStackTrace();
		}
		return null;
	}

	/**
	 * 使用模和指数生成RSA私钥 注意：【此代码用了默认补位方式，为RSA/None/PKCS1Padding，不同JDK默认的补位方式可能不同，如Android默认是RSA/None/NoPadding】
	 * @param modulus 模
	 * @param exponent 指数
	 * @return
	 */
	public static RSAPrivateKey getPrivateKey(String modulus, String exponent) {
		try {
			BigInteger b1 = new BigInteger(modulus);
			BigInteger b2 = new BigInteger(exponent);
			KeyFactory keyFactory = KeyFactory.getInstance(RSA);
			RSAPrivateKeySpec keySpec = new RSAPrivateKeySpec(b1, b2);
			return (RSAPrivateKey) keyFactory.generatePrivate(keySpec);
		} catch (NoSuchAlgorithmException e) {
			e.printStackTrace();
		} catch (InvalidKeySpecException e) {
			e.printStackTrace();
		}
		return null;
	}

	/**
	 * 公钥加密
	 * @param data
	 * @param publicKey
	 * @return
	 */
	public static String encryptByPublicKey(String data, RSAPublicKey publicKey) {
		try {
			Cipher cipher = Cipher.getInstance(RSA);
			cipher.init(Cipher.ENCRYPT_MODE, publicKey);
			// 模长
			int key_len = publicKey.getModulus().bitLength() / 8;
			// 加密数据长度 <= 模长-11
			String[] datas = splitString(data, key_len - 11);
			String mi = "";
			// 如果明文长度大于模长-11则要分组加密
			for (String s : datas) {
				mi += bcd2Str(cipher.doFinal(s.getBytes()));
			}
			return mi;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	/**
	 * 私钥解密
	 * @param data
	 * @param privateKey
	 * @return
	 */
	public static String decryptByPrivateKey(String data, RSAPrivateKey privateKey) {
		try {
			Cipher cipher = Cipher.getInstance(RSA);
			cipher.init(Cipher.DECRYPT_MODE, privateKey);
			// 模长
			int key_len = privateKey.getModulus().bitLength() / 8;
			byte[] bytes = data.getBytes();
			byte[] bcd = ASCII_To_BCD(bytes, bytes.length);
			System.err.println(bcd.length);
			// 如果密文长度大于模长则要分组解密
			String ming = "";
			byte[][] arrays = splitArray(bcd, key_len);
			for (byte[] arr : arrays) {
				ming += new String(cipher.doFinal(arr));
			}
			return ming;
		} catch (Exception e) {
			e.printStackTrace();
		}
		return null;
	}

	/**
	 * ASCII码转BCD码
	 */
	private static byte[] ASCII_To_BCD(byte[] ascii, int asc_len) {
		byte[] bcd = new byte[asc_len / 2];
		int j = 0;
		for (int i = 0; i < (asc_len + 1) / 2; i++) {
			bcd[i] = asc_to_bcd(ascii[j++]);
			bcd[i] = (byte) (((j >= asc_len) ? 0x00 : asc_to_bcd(ascii[j++])) + (bcd[i] << 4));
		}
		return bcd;
	}

	private static byte asc_to_bcd(byte asc) {
		byte bcd;

		if ((asc >= '0') && (asc <= '9')) bcd = (byte) (asc - '0');
		else if ((asc >= 'A') && (asc <= 'F')) bcd = (byte) (asc - 'A' + 10);
		else if ((asc >= 'a') && (asc <= 'f')) bcd = (byte) (asc - 'a' + 10);
		else bcd = (byte) (asc - 48);
		return bcd;
	}

	/**
	 * BCD转字符串
	 */
	private static String bcd2Str(byte[] bytes) {
		char temp[] = new char[bytes.length * 2], val;

		for (int i = 0; i < bytes.length; i++) {
			val = (char) (((bytes[i] & 0xf0) >> 4) & 0x0f);
			temp[i * 2] = (char) (val > 9 ? val + 'A' - 10 : val + '0');

			val = (char) (bytes[i] & 0x0f);
			temp[i * 2 + 1] = (char) (val > 9 ? val + 'A' - 10 : val + '0');
		}
		return new String(temp);
	}

	/**
	 * 拆分字符串
	 */
	private static String[] splitString(String string, int len) {
		int x = string.length() / len;
		int y = string.length() % len;
		int z = 0;
		if (y != 0) {
			z = 1;
		}
		String[] strings = new String[x + z];
		String str = "";
		for (int i = 0; i < x + z; i++) {
			if (i == x + z - 1 && y != 0) {
				str = string.substring(i * len, i * len + y);
			} else {
				str = string.substring(i * len, i * len + len);
			}
			strings[i] = str;
		}
		return strings;
	}

	/**
	 * 拆分数组
	 */
	private static byte[][] splitArray(byte[] data, int len) {
		int x = data.length / len;
		int y = data.length % len;
		int z = 0;
		if (y != 0) {
			z = 1;
		}
		byte[][] arrays = new byte[x + z][];
		byte[] arr;
		for (int i = 0; i < x + z; i++) {
			arr = new byte[len];
			if (i == x + z - 1 && y != 0) {
				System.arraycopy(data, i * len, arr, 0, y);
			} else {
				System.arraycopy(data, i * len, arr, 0, len);
			}
			arrays[i] = arr;
		}
		return arrays;
	}

	public static void main(String[] args) {
		try {
			Map<String, Object> map = RsaUtils.getKeys();
			RSAPublicKey publicKey = (RSAPublicKey) map.get("public");
			RSAPrivateKey privateKey = (RSAPrivateKey) map.get("private");

			// 模
			String modulus = publicKey.getModulus().toString();
			System.out.println(modulus);
			// 公钥指数
			String public_exponent = publicKey.getPublicExponent().toString();
			System.out.println(public_exponent);
			// 私钥指数
			String private_exponent = privateKey.getPrivateExponent().toString();
			System.out.println(private_exponent);
			// 明文
			String ming = "hello world";
			// 使用模和指数生成公钥和私钥
			RSAPublicKey pubKey = RsaUtils.getPublicKey(modulus, public_exponent);
			RSAPrivateKey priKey = RsaUtils.getPrivateKey(modulus, private_exponent);
			// 加密后的密文
			String mi = RsaUtils.encryptByPublicKey(ming, pubKey);
			System.out.println(mi);
			// 解密后的明文
			ming = RsaUtils.decryptByPrivateKey(mi, priKey);
			System.out.println(ming);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}

}
